Automatic teller equipment has become well accepted as the versatile means through which customers can conduct basic banking business at any time and at diverse locations away from the bank. The number of such automatic teller units is likely to increase dramatically in the future, at substantial expense to the banks and institutions that operate them, without fully satisfying customers' demands for banking services available at any time and at any location where the customer may be.
Additionally, point-of-sale terminals are rapidly increasing in number and popularity among retailers who rely on them as versatile means for completing sale transactions with non-cash paying customers. Such customers prefer to pay with credit cards or checks which, in turn, are also tied to banks at diverse locations. The non-cash-paying customer, therefore, must rely on checks or credit cards as token indications of his established business relationship with his banking institution, and neither the retailer nor the customer can directly or immediately involve their respective banking institutions to transfer value from the customer to the retailer during the process of completing the transaction. Data communications schemes over unsecured channels are known from the literature (see, for example, U.S. Pat. Nos. 4,283,599; 4,281,215; 4,268,715; and 4,315,101), but these schemes may not be adequate for actually transferring funds on deposit from one account to another.